One known method for abating certain diesel engine exhaust constituents is by use of an exhaust after-treatment system that utilizes Selective Catalytic Reduction (SCR) of nitrogen oxides. In a typical SCR system, diesel exhaust fluid (DEF), which may include urea or a urea-based water solution, is mixed with exhaust gas before being provided to an appropriate catalyst. In some applications, the DEF is injected directly into an exhaust passage through a specialized injector device. In the case of urea, the injected DEF mixes with exhaust gas and breaks down to provide ammonia (NH3) in the exhaust stream. The ammonia then reacts with nitrogen oxides (NOx) in the exhaust at a catalyst to provide nitrogen gas (N2) and water (H2O).
As can be appreciated, SCR systems require the presence of some form of DEF sufficiently close to the engine system such that the engine can be continuously supplied during operation. Various DEF delivery systems are known and used in engine applications. In known DEF injection systems, a reservoir is installed onto a vehicle for containing the DEF, which is drawn from the reservoir and delivered in metered amounts to the engine exhaust system. The reservoir has a finite urea capacity such that periodic replenishment of the DEF within the reservoir is required. In certain applications, such as mining, construction, farming and other field applications, DEF replenishment may be carried out in the work environment of the machine. Such refilling or replenishment operations are typically carried out by dispensing DEF into the reservoir through a removable reservoir cap. As can be appreciated, dirt and other debris may fall within the reservoir, especially during a refilling operation, which may present problems if the dirt and/or other debris is ingested into a pump drawing DEF from the reservoir, and/or is delivered with the DEF to the DEF injector, which typically has close clearances and small injection orifices that can bind or become plugged by the debris.
In the past, various solutions have been proposed to mitigate the presence of debris within a DEF container. Most such solutions propose adding filtering media to a fill opening of the container, or adding filters in line with a DEF supply line within the system at a location upstream of a DEF pump and/or before the DEF injector. However, such known solutions present certain challenges. For example, a filter disposed at an inlet of the container may impede the rapid filling of the container, which is desired, especially since a lengthy filling process may rob the machine of profitable time in service. Moreover, the aqueous components of DEF fluids are susceptible to thermal effects such as breakdown at high temperatures or freezing at low temperatures, which makes their presence in lengthy in-line supply conduits and/or filters undesirable due to crystallization effects and/or freezing within the filter. Such conditions, which require the addition of heaters and/or other temperature control devices to be added to DEF supply systems increase the cost and complexity of those systems.